Atticus's Odyssey: Reincarnated Into A Playground - Chapter 7: Getting stronger

Shuu is a member of the literary club that can’t write. One day, he gets a mysterious message on his phone from a girl called Eina, and from that impulsive contact, they begin to exchange messages. They talk of things like their shared interest in novels and grow close. However, when they try and meet, they discover a shocking truth. Eina lives… not in the present, but five years in the past! How will their love develop, parted by five years of nights…!?

A striking man of mysterious origin and peerless talent, he looks back at the world, in all its entirety, with utter disdain. And yet, in the treacherous and unpredictable ultimate formation of the Boundless Secular World, he guards a breathtaking ancient qin with broken strings, waiting silently for the destined one to arrive!

A boy encounters him, and knows for the first time that the world beneath the Heavens is a fickle place. Not even demons, devils, ghosts and monsters can match the frivolity of human nature!

A slender physique, and jade-like beauty, but the sword that strikes between heaven and earth is not unlike a streaming rainbow!

The vastness of the starry sky, the seven emotions and six desires! Greed, anger and ignorance! The teachings of Buddha will grant you boundless strength!

A sea of blood will come, at the cost of all mortal beings full of honest hope!

The ghosts wail as the gods roar, but the sea of blood has no end!

Where, pray tell, is the path I should take?

Since there is no path, no matter how bitter and bloody the sea, even if my boat is made out of bones, I will soar to the heavens above!

- Description from Novelupdates

Seven years ago, after their breakup, he disappeared without a trace.